The present invention relates to a method of regulating the temperature, by which the temperature of heated bodies having different heat capacities can be always regulated to a predetermined constant temperature.
When bodies to be heated (hereinafter referred to as bodies) are heated at a predetermined temperature by a heater, in general, the required amount of heat changes depending upon the initial temperature of the bodies, heat quantity of the heater, ambient temperature of the bodies, and the heat capacities of the bodies. In particular, when the heater is not in contact with the bodies but a finite gap exists therebetween, or when bodies have different sizes, weights and specific heats, for maintaining the bodies at a predetermined temperature at all times, it is necessary to find the heating conditions through experiments and to determine the heat quantity of the heater each time.
However, when bodies having different heat capacities and, particularly, having different sizes, different weights and/or different specific heats, are successively passed through the steps, it is required to change the heat quantity of the heater every time.
The greater the heat capacity of the heater, however, the slower the response speed of the heater in regard to its temperature. In the case of a heater having output of about 6 KW, for instance, a time of about 20 minutes is required to raise the temperature from room temperature to about 250.degree. C., and a time of about 5 minutes is required to lower the temperature from about 250.degree. C. to about 200.degree. C.
Therefore, the control method becomes quite difficult where it is desired to heat bodies that flow successively through the steps and that have different sizes, different weights and different specific heats, e.g., where it is desired to heat panels of color picture tubes having such different sizes as 14 inches, 20 inches, 26 inches and the like at a predetermined temperature and at high speeds at all times.
That is, in manufacturing color picture tubes, as is well known, the panel temperature serves as the most important process factor in the process for forming phosphor screens such as in the step of forming black (light-absorbing) matrix and in the step of applying phosphor, and seriously affects three requirements, i.e., affects characteristics, yields and quality of the products.
A panel of 6-inch picture tube weighs 316 grams and has a maximum diameter of 150 mm, and a panel of 26-inch picture tube weighs 13610 grams and has a maximum diameter of 663 mm. Here, if the heater has an output of 6 KW and the distance is 100 mm between the panel and the heater, the temperature elevating rate (dT/dt, where T denotes the temperature and t denotes the time) per unit time is 2.4.degree. C./sec. for the panel of 6-inch picture tube and 0.08.degree. C./sec. for the panel of 26-inch picture tube, the difference being about 40 times.